Interface identification of the solid electrolyte interphase on graphite

TL;DR

This study uses Density Functional Theory to identify stable lithium carbonate-graphite interfaces, revealing key structural features and charge distributions that influence interface stability and lithium transport in batteries.

Contribution

It introduces specific interface models with detailed structural and energetic analysis, highlighting the importance of (a,b)-oriented Li2CO3 slabs for stable interfaces.

Findings

(a,b)-oriented Li2CO3 slabs promote strong binding with graphite.

Charge distribution induces an electric potential gradient at the interface.

Interfacial lithium diffusion is mainly through interstitials.

Abstract

By means of Density Functional Theory calculations we evaluate several lithium carbonate - graphite interface models as a prototype of the Solid Electrolyte Interphase capping layer on graphite anodes in lithium-ion batteries. It is found that only an (a,b)-oriented Li2CO3 slab promotes tight binding with graphite. Such mutual organization of the components combines their structural features and reproduces coordination environment of ions, resulting in an adhesive energy of 116 meV/{\AA}2 between graphite and lithium carbonate. This model also presents a high potential affinity with bulk. The corresponding charge distribution at such interface induces an electric potential gradient, such a gradient having been experimentally observed. We regard the mentioned criteria as the key descriptors of the interface stability and recommend them as the principal assessments for such interface study. In addition, we evaluate the impact of lithiated graphite on the stability of the model interface and study the generation of different point defects as mediators for Li interface transport. It is found that Li diffusion is mainly provided by interstitials. The induced potential gradient fundamentally assists the intercalation up to lithiation ratio of 70%.